--- title: "Getting 25 Gbps Thunderbolt Ethernet on my Mac Studio" url: https://daily.dev/posts/getting-25-gbps-thunderbolt-ethernet-on-my-mac-studio-ka6fhct9b source_url: https://www.jeffgeerling.com/blog/2026/getting-25g-ethernet-mac-thunderbolt type: article source: "Jeff Geerling" published: 2026-07-31T14:10:09.751Z updated: 2026-08-01T18:18:16.806Z tags: ["networking", "mac"] reading_time: 5 upvotes: 1 comments: 0 language: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Getting 25 Gbps Thunderbolt Ethernet on my Mac Studio **[Jeff Geerling](https://daily.dev/sources/jeffgeerling)** · 5 min read · 1 upvotes · 0 comments ## Summary Jeff Geerling documents his experience adding 25 Gbps Ethernet to a Mac Studio via a cheap OCP 2 NIC with a Thunderbolt 3 adapter board. The adapter cost around $160-$299 compared to $999+ commercial options. Two main challenges arose: an outdated iperf3 on the NAS capping speeds at 15 Gbps (fixed by recompiling), and severe overheating of the passively-cooled enclosure. The thermal fix involved designing and 3D-printing a custom fan duct in Noctua-branded PLA, mounting an 80mm Noctua 5V fan, and soldering power directly from the PCB. Final temperatures dropped below 36°C. Real-world Samba transfer speeds reached ~1.4 GB/s read and ~1 GB/s write — only a modest improvement over the built-in 10G Ethernet, raising questions about whether the effort was worthwhile. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Community take How the wider developer community reacted, aggregated from 1 discussion and 113 comments across hackernews (as of 2026-08-01). **TL;DR:** Commenters are broadly interested in the 25GbE-over-Thunderbolt setup but quickly pivot to technical caveats: macOS SMB/RDMA limitations are the real bottleneck, the NIC's age and process node explain the heat, and cheaper DIY alternatives (eGPU dock + ConnectX-4) exist for ~$150-200. **Sentiment:** 45% positive · 35% mixed · 20% skeptical **The case for** - macOS now supports RDMA over Thunderbolt (since March 2025), opening a path to SMB Direct in the future. - A DIY eGPU-dock approach can achieve similar speeds for ~$150-200 using second-hand parts. - iperf3 results confirm the link itself can hit full 25 Gbps line rate, so the hardware works. - USB4/Thunderbolt point-to-point networking is a viable, cheap alternative for two-machine setups at up to 40-80 Gbps. **The pushback** - macOS SMB implementation is widely regarded as poor—stalls, disconnections, and no RDMA support in the SMB stack yet. - The ConnectX-4 NIC used is ~12 years old and built on an old process node, explaining excessive heat. - The Sonnet TB5 chassis bundle is seen as overpriced ($600 premium for a NIC that shouldn't cost that much). - RTL8156-based USB-C multi-gig dongles are reported as unreliable on Apple Silicon Macs by multiple commenters. - Apple has deprioritized high-speed wired networking for professionals, abandoning PCIe slots and first-party >1GbE NICs. **By community** - hackernews (mixed): Enthusiastic about the concept but heavily focused on macOS SMB/RDMA limitations, NIC heat explained by old process node, and cheaper DIY alternatives that achieve similar results. **Hottest debate:** Whether macOS's lack of SMB Direct/RDMA support is the true bottleneck and whether Apple will ever prioritize high-speed wired networking for professionals. **Open questions** - Will Apple update its SMB driver to leverage the new Thunderbolt RDMA support for real-world file transfer speeds? - Is a single-chip USB4↔25GbE NIC (without a PCIe bridge hop) available yet? - Would a Thunderbolt-native network switch (e.g., from Mikrotik) be a viable product? **Highlights** > This is a ConnextX4 on a thunderbolt bridge. This is well trodden territory. Unless some hero of open source has come to bat recently, MacOS doesn't support RDMA with this card or over Ethernet at all for that matter. It's only supported over Thunderbolt. His iperf3 results show that it's able to go full beans on a single 25g port. A cross platform SMB file copy is kind of a meaningless benchmark in this context. IMO a pretty cool product would be a network switch providing native thunderbolt interfaces to multiple upstream hosts. That wouldn't magically fix this RDMA issue, though. This is just a separate thought. Seems like the kind of thing Mikrotik should make. > — [gorkish on hackernews · 1 comments](https://news.ycombinator.com/item?id=49126645) > I have a 25GbE setup using Thunderbolt, kinda similar to the author's. Except that my fan is held together by a piece of string, not a 3D-printed enclosure. I found that SMB on macOS is just bad. If I try to heavily load it (e.g. by doing mass conversions in my Audible library), it can cause stalls and disconnections. I managed to find a set of parameters (in /etc/nsmbd.conf) that makes it work more-or-less reliably by trial-and-error: dir_cache_off=yes, file_ids_off=yes, notify_off=yes, mc_on=no. It's still terrible, though. It's so bad that Linux in a Parallels VM works _better_. > — [cyberax on hackernews · 1 comments](https://news.ycombinator.com/item?id=49126691) > It's distance. 25GbaseT is good for 30m+. Thunderbolt is good for 1m without active cables. Making the much more rugged signal is a much more intense job. And your computer already speaks the PCIe and thunderbolt. It has that probably on CPU. Here we have to receive USB, convert it to Ethernet. On much less up to date process nodes than your CPU. Third, until very recently for even 10Gbit it meant using a usb4<->pcie bridge chip which itself was hot, to provide a generic pcie connection, which then talked to a conventional network chip, so it was a double hop: USB <-> pcie <-> nic. I don't know if 25Gbit to USB direct convert is available yet but we've seen a wave of vastly cheaper 10Gbit adapters come out that are single chip USB<->nic, probably not pcie at all, that are much much cooler. 25Gbit is probably still not here yet, maybe? > — [jauntywundrkind on hackernews](https://news.ycombinator.com/item?id=49126715) > For us <25Gbps plebes out there: For god's sake do not buy a USB-C RealTek RTL8156-equipped multi-gig ethernet dongle to use with your Mac. I went through 3, and they're all trash: Plugable 2.5G USB-C to ethernet adapter (bought November 2025), SABRENT USB C to 2.5Gbps ethernet adapter (bought October 2024), UGREEN USB C 2.5G ethernet adapter (also October 2024). In my experience they immediately fall on their face in a speedtest and drop to a couple hundred Mbps, experience packet loss, etc. This is testing across a few modern Apple Silicon Macs. I now have a WavLink WL-NWU341G 5Gbps dongle with the RTL-8157 that seems to work well, but I've only run a couple of tests-- I am away from my home setup and don't have wired ethernet run to all the rooms where I'm living. If you do some Googling, there's some good information out there about it, but when I bought the bad ones, I couldn't find any information corroborating my experience. > — [rconti on hackernews · 3 comments](https://news.ycombinator.com/item?id=49129022) > The Mac Studio in most of my videos is my own workstation, purchased a while back. The 4 Mac Studio cluster I tested with Exo and Thunderbolt RDMA was a loaner cluster from Apple. There's no universe in which I could justify buying that. I always mention any equipment that's provided / loaned / etc. and the nature of my relationships with vendors—I try to also keep this document updated for transparency's sake: https://github.com/geerlingguy/youtube/blob/master/Sponsors.... > — [geerlingguy on hackernews · 1 comments](https://news.ycombinator.com/item?id=49129087) **Source threads** - [hackernews](https://news.ycombinator.com/item?id=49125034) · 41 points · 113 comments ## Similar posts on daily.dev - [New 10 GbE USB adapters are cooler, smaller, cheaper](https://daily.dev/posts/new-10-gbe-usb-adapters-are-cooler-smaller-cheaper-9q5yp1afn) · Jeff Geerling · 0 upvotes · 0 comments - [Reliable 25 Gigabit Ethernet via Thunderbolt](https://daily.dev/posts/reliable-25-gigabit-ethernet-via-thunderbolt-n75o5qzli) · Hacker News · 0 upvotes · 0 comments --- Tags: [#networking](https://daily.dev/tags/networking), [#mac](https://daily.dev/tags/mac) [View this post on daily.dev](https://daily.dev/posts/getting-25-gbps-thunderbolt-ethernet-on-my-mac-studio-ka6fhct9b)